1. Field of the Invention
The present invention relates to a golf club head.
2. Description of the Related Art
In general, a plurality of parallel linear grooves are formed in the face surface of a golf club head to extend in the toe-to-heel direction. These grooves are called, for example, scorelines, marking lines, or face lines (they will be referred to as scorelines in this specification). These scorelines have an effect of increasing the back spin amount on a struck golf ball, or suppressing a significant decrease in back spin amount on a struck golf ball upon a shot in rainy weather or that from the rough.
A rule concerning the scorelines of an athletic golf club head stipulates that the edge of each scoreline must fall within a virtual circle which has a radius of 0.011 inches and is concentric with a virtual circle which has a radius of 0.010 inches and is inscribed in both the side wall of this scoreline and the face surface (to be referred to as the “two-circle rule” hereinafter). To comply with the two-circle rule, it is effective to, for example, chamfer the edges of the scorelines.
Unfortunately, when the edges of the scorelines are chamfered, the back spin amount on a struck golf ball decreases. Under the circumstance, techniques of forming grooves finer than the scorelines in the face surface have been proposed (for example, Japanese Patent Laid-Open No. 2007-202633). These fine grooves are effective in preventing a decrease in back spin amount on a struck golf ball.
However, when grooves finer than the scorelines are formed in the face surface, a variation in back spin amount may occur depending on the position of a striking point. An advanced golfer who has a keen sense may feel uncomfortable with this variation albeit small.